Previously, the LB method (Langmuir Blodgett method) or a liquid phase adsorption method was used to form a monomolecular film. In the LB method, a straight chain molecule having a hydrophilic group and a water-repelling group are layered on a water surface, and the water is manipulated to deposit the layer on a substrate surface. In the LB method, which is essentially a wet process, a monomolecular film is fixed to the substrate by only Van der Waals' force, and the mechanical strength is weak. The chemical adsorption method using a liquid phase is a method of forming a monomolecular film via silicon bonding. The method includes dipping and holding a substrate in a non-aqueous solvent in which a molecule containing a carbon chain and an active silane group at one end is reacted with an active hydrogen of a hydroxyl group on the surface of the substrate. The principle of forming a chemically adsorbed monomolecular film in the above solution is to form a monomolecular film by initiating a dehydrochlorination reaction between a hydroxyl group on the surface of the substrate and a chlorosilyl group of the chlorosilane based adsorbent. In this manufacturing method, a monomolecular film can be obtained by dipping and holding a substrate such as a metal in an adsorptive liquid in a which chlorosilane based surface active material is dissolved in a non-aqueous solvent. (For reference, see the specification of U.S. Pat. No. 4,673,474, J. Am. Soc. 1983, 105, 674-676 (Sagiv), "Thin solid Films", 99 (1983) 235-241(Sagiv), "The American Physical Society" Vol.39, No.7 (1989)).
The chemically adsorbed monomolecular film, which can be obtained by the above method, bonds to the surface of the substrate via a strong chemical bond. The film does not separate from the substrate as long as the surface of the substrate is not scraped. However, this method is a wet process, utilizing a chemical reaction in a solvent in the liquid state. The chemical adsorption method using a liquid phase requires two to three hours to absorb at room temperature and to form a satisfactory adsorbing film since the adsorbing reagent is diluted with solvent. In addition, in the wet method, the types of solvent and substrates for adsorption are very severely limited since some of substrates can be damaged by the solvent or hydrochloric acid which is generated during the adsorption reaction.
Furthermore, the diluted solvent often contains minute particles of dust, and pinholes are easily generated in an ultra thin film. In addition, the substrate itself may swell or be dissolved by some types of diluted solvents.
Furthermore, in forming a monomolecular film by the wet process mentioned above, contamination of the liquid solution cannot be easily avoided. For example, in forming a monomolecular film for an electronic device, such as an insulated film for a condenser, electronic, optical or precision parts such as a protective film for a laser disk, contamination must be avoided as much as possible. In forming a thin film by deposition on a monomolecular film, the wet process requires washing and drying of the substrate. As a result, contamination and the number of days are increased.
On the other hand, there are dry processes for forming organic ultra thin films, such as plasma polymerization and vacuum deposition methods. In these methods, the types of molecules which can be obtained are limited very severely, and forming a monomolecular film can be very difficult.
This invention provides a method of forming a monomolecular film by a method using a gas phase to solve the above problems.
Furthermore, this invention aims to provide a method in which the type of substrate is not limited, an adsorbing solvent is not required, and an adsorbed film can be formed effectively in a short time. This invention prevents pinholes and forms a chemically adsorbed, uniformly thin film firmly on a substrate. This film formation is also more efficient.